The selection of behaviorally relevant stimuli from such crowded visual scenes is mediated by visual attention. Disorders of attention; are frequently accompanied by behavioral deficits and mental diseases. The question of how the competition among multiple stimuli is resolved is central to understanding the neural basis of visual attention. This proposal aims to develop new analytical tools to achieve a detailed understanding of the dynamic informational transactions that underlie selective visual attention processing in the cerebral cortex. Here we propose a novel approach effectively dealing with problems of non-linearity and non-stationary based on the concepts of entropy analysis. The information theory techniques provide a quantitative measure of the time rate of information flow within and between cortical sites. This methodology consists of a number of interrelated techniques that can characterize the detailed time course of cortical activation and the multiple, complex interactions of cortical networks. Specific hypotheses concerning the dynamics of coordinated neuronal ensembles will be tested by analysis of local field potentials previously recorded from indwelling electrodes in the cerebral cortex of non-human primates performing a visual spatial attention task. Advances in information theory technology will be utilized to derive a quantifiable entropy measure of the rapidly changing cortical activation, to relate the entropy quantity to behavioral measure, and to measure causal influences between cortical sites. This work is expected to: (1) produce new insights into the functional dynamics in the cortex during visual perception, motor performance, and visual spatial attention; and (2) make available novel information-theoretic tools for the investigation of large-scale neural systems in a variety of neurocognitive processes.